JP4241963B2

JP4241963B2 - Information recording / reproducing device

Info

Publication number: JP4241963B2
Application number: JP23891898A
Authority: JP
Inventors: 青児西脇
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1997-08-29
Filing date: 1998-08-25
Publication date: 2009-03-18
Anticipated expiration: 2018-08-25
Also published as: JPH11134696A

Description

【０００１】
【発明の属する技術分野】
本発明は、高密度の情報を記録もしくは再生する装置に関するものである。
【０００２】
【従来の技術】
従来の技術について、例えばＳＮＯＭ（スキャンニングニアーフィールドオプチカルマイクロスコープ(Scanning Near-Field Optical Microscope)）と呼ばれるホサカ(S.Hosaka)等によるJ.Vac.Sci.technol.B13(1995)2813に記載の情報記録再生装置に基づいて説明する。図９は従来の情報記録再生装置の断面構成図である。高屈折率のコア２５と、それを取り巻く低屈折率のクラッド２６とで構成された光ファイバーは、コアの先端が円錐状に削り込まれ、それを取り巻くようにクラッド２６と反射膜２７とが形成されている。この円錐部の先端はわずかなギャップδを隔てて、ディスク基板１３上に形成された記録膜１４に対面している。
【０００３】
ギャップδは５０ｎｍ以下の微小量で、円錐先端部のコア直径は０．１μｍ程度である。この光ファイバーに放射光源の光を入力すると、円錐先端部からエバネッセント光２９がにじみ出る。円錐先端部が記録膜１４に近接しているため、例えば記録膜１４が相変化性の膜であれば、エバネッセント光２９の熱エネルギーにより記録膜上に周囲と異なる反射率の信号マーク１９を形成できる。また、記録膜１４からの反射散乱光３０を光検出器３１で検出することで、信号マーク１９の有無を判定できる。
【０００４】
以上の情報記録再生装置により、円錐先端部のコア直径に相当した信号記録と信号再生が可能となり、例えば信号マーク１９の直径を０．１μｍとすると、ディジタルビデオディスク（以下ＤＶＤと称す）（信号マークの直径は０．３〜０．４μｍ程度）に比べ１０倍以上の高密度の情報記録再生装置を提供できる。
【０００５】
このような従来の情報記録再生装置では、例えば図１０Ａ及び図１０Ｂに示すような問題点があった。図１０Ａは、従来の情報記録再生装置の主要部と、図１０Ｂは、同装置の光伝搬方向（−ｚ軸）に沿った光エネルギー分布図を示す。
【０００６】
図１０Ａにおいて、光ファイバーを伝搬する導波光２８は、円錐部の手前までは（ｚ＞ａ）ほとんど損失なく伝搬するが、円錐部では（ａ＞ｚ＞０）入射光２８ａが屈折光２８ｂと反射光２８ｃに分かれ、反射光２８ｃは再び屈折光と反射光に分かれ、以上のことを円錐部の長さａに渡って何度も繰り返すので、円錐部の先端から放出されるエバネッセント光２９は極めて弱くなる。
【０００７】
一般に円錐部の前での導波光の光エネルギーを１とすると、円錐部の先端から放出されるエバネッセント光２９の光エネルギーηは、１０^-7〜１０^-5程度と言われ、例えば図１０Ｂに示すように極めて光利用効率が低い。従って、記録膜１４を記録するためには長い時間を要し、情報記録装置として使うには記録の高密度化の反面、情報転送速度の大幅な低下という犠牲を払うことになる。
【０００８】
また、円錐部の先端（ヘッド）は、いわば空間に浮かんだ点のようなもので、熱集中が起こりやすく、熱損傷による劣化が起こりやすい。さらに、ヘッドを記録面１４に近接させながら安定に走査させるには、複雑なメカニズムが必要なうえ、記録面上のトラックを認識できないのでトラック方向の高密度化が困難である。
【０００９】
また、反射散乱光３０を用いた再生原理は空間的に広い広がりをなす反射散乱光のごく一部を検出することから、その再生感度は極めて悪い。
【００１０】
【発明が解決しようとする課題】
本発明はかかる問題点に鑑み、光利用効率を大幅に向上させ、熱損傷による劣化がなく、ヘッドを信号面に近接させながら安定に走査させることが可能で、信号面上のトラックを認識して制御でき、信号再生感度を大幅に高められる情報記録再生装置を提供することを目的とする。
【００１１】
【課題を解決するための手段】
前記目的を達成するため、本発明の第１番目の情報記録再生装置は、放射光源と、透明基板と、この透明基板の光源と反対側にある表面の上に構成された導波層と、導波層の界面上に形成され光軸を中心とする同心円状の周期構造を持つ光結合手段とからなり、導波層は周期構造の中心位置で断絶し、放射光源からの光は光結合手段により導波層内で周期構造の外周側から中心に伝搬する導波光を励起し、この導波光は導波層の断絶位置においてその一部が導波層に近接して置かれた平面基板上の信号面に漏れ出ることを特徴とする。
【００１２】
この構造により、透明基板は放射光源と同一構造体の上に固定され、この構造体は押圧手段により信号面に押さえつけられながら相対的に移動できる。
次に本発明の第２番目の情報記録再生装置は、放射光源と、前記放射光源から出射する光を平行光に変換する集光手段と、前記平行光の光軸を中心軸とする透明円錐体と、前記円錐体の低面部に形成された透明バッファー層と、前記バッファ層上に形成された導波層とからなり、前記導波層は前記円錐体の中心軸位置で断絶し、前記円錐体の屈折率と前記導波層の屈折率とバッファー層の屈折率とはこの順に小さくなる関係にあり、前記平行光は前記円錐体の円錐面を屈折して前記バッファー層を経て前記導波層に入射して、前記導波層内で外周側から中心軸側に伝搬する導波光を励起し、前記導波光は前記断絶位置においてその一部が前記導波層に近接して置かれた平面基板上の信号面に漏れ出ることを特徴とする。
【００１３】
この構造により、円錐体が放射光源及び集光手段と同一構造体の上に固定され、この構造体は押圧手段により信号面に押しつけられながら相対的に移動できる。
【００１４】
前記した本発明の第１番目の情報記録再生装置においては、前記透明基板が前記放射光源と同一構造体の上に固定され、前記構造体は押圧手段により前記信号面に押さえつけられながら相対的に移動し、この移動により前記導波層表面が前記信号面と対面しながら空気層を挟んで前記構造体が浮上することが好ましい。
【００１５】
前記した本発明の第２番目の情報記録再生装置においては、前記円錐体が、前記放射光源及び前記集光手段と同一構造体の上に固定され、前記構造体は押圧手段により前記信号面に押しつけられながら相対的に移動し、この移動により前記導波層表面が前記信号面と対面しながら空気層を挟んで前記構造体が浮上することが好ましい。
【００１６】
また前記した本発明の第１〜２番目の情報記録再生装置においては、前記導波層上には、前記導波層よりも低屈折率の第１の透明層が積層されていることが好ましい。
【００１７】
また前記装置においては、前記第１の透明層上には、前記断絶位置を除いた位置で反射層が積層されていることが好ましい。
また前記装置においては、前記第１の透明層上には、強い光の照射によって不透明から透明に変化するマスク層が積層されていることが好ましい。
【００１８】
また前記装置においては、前記断絶位置において、前記断絶部が前記導波層よりも高屈折率の第２の透明層で覆われ、前記第２の透明層を介して前記導波層内の導波光が前記信号面側に漏れ出ることが好ましい。
【００１９】
また前記装置においては、前記第２の透明層上には、強い光の照射によって不透明から透明に変化するマスク層が積層されていることが好ましい。
また前記装置においては、前記断絶部の形状が、前記光軸を中心軸とする円錐状及び円錐台状からえばれる少なくとも一つの形状であることが好ましい。
【００２０】
また前記装置においては、前記断絶位置において、前記導波層から前記信号面側に漏れ出る光により、前記信号面上に信号マークを記録することが好ましい。また前記装置においては、前記透明基板上又はその近傍に光検出器を形成し、前記断絶位置において前記導波層から前記信号面側に漏れ出る光が前記信号面を反射し、この反射光の一部を前記光検出器で検出し、前記信号面上に形成された信号を再生することが好ましい。
【００２１】
また前記装置においては、前記光検出器は、前記信号面の移動方向に直交する分割線で等分割されており、前記等分割間の差分信号を再生信号とすることが好ましい。
【００２２】
また前記装置においては、前記信号面上に前記信号面の移動方向に沿った凹凸構造が形成されており、前記光検出器は前記移動方向に沿った分割線で等分割されており、前記等分割間の差分信号をトラッキング制御信号とすることが好ましい。
【００２３】
また前記装置においては、前記透明基板上又はその近傍に光検出器を形成し、前記断絶位置において前記導波層から前記信号面側に漏れ出る光が前記信号面を反射して再び前記導波層内に取り込まれ、前記導波層内を周期構造の中心から外周側に伝搬する導波光となり、前記導波光または前記導波層から放出される光の少なくとも何れか一方を前記検出器で検出し、前記信号面上に形成された信号を再生することが好ましい。
【００２４】
また前記装置においては、前記光検出器は、前記信号面の移動方向に直交する直線を間に挟む２つの部分から構成され、この２つの検出器の差分信号を再生信号とすることが好ましい。
【００２５】
また前記装置においては、前記信号面上に前記信号面の移動方向に沿った凹凸構造が形成されており、前記光検出器は前記移動方向に沿った直線に関して対称な２つの部分から構成され、前記２つの検出器の差分信号をトラッキング制御信号とすることが好ましい。
【００２６】
また前記装置においては、前記断絶位置において前記導波層から前記信号面側に漏れ出る光が、前記信号面を反射して再び前記導波層内に取り込まれ、導波層内を周期構造の中心から外周側に伝搬する導波光となり、前記導波光が再び前記放射光源に帰還し、この帰還によって発生する前記放射光源の駆動特性の変化を検出し、前記信号面上に形成された信号を再生することが好ましい。
【００２７】
また前記装置においては、前記導波層を多層膜で構成し、導波層内を伝搬する導波光の等価屈折率がＴＥモードとＴＭモードとでほぼ等しくすることが好ましい。
【００２８】
また前記装置においては、前記導波層を構成する多層膜が、低屈折率の透明層の間に高屈折率の透明層を挟んだ３層構造で形成することが好ましい。
また前記装置においては、前記導波層を構成する多層膜が、高屈折率の透明層の間に低屈折率の透明層を挟んだ３層構造で形成することが好ましい。
【００２９】
【発明の実施の形態】
前記した本発明において、外部入力による導波光の発生は、いわば共振条件（入力条件）を満たす場合に限られ、この条件を満たすときに入力光（放射光からの光）の一部が導波光に変換される。これを”励起する”という。
【００３０】
また、入力光（放射光からの光）の一部が導波光に変換されるので、外周面で入射光から変換された導波光の積分が、内周側の導波光となる。当然のことながら、現在導波している任意の位置でも入力光が導波光に変換されて、それまで伝搬していた導波光に加わる。
【００３１】
また、前記した本発明において、”光結合手段”は、入力光（放射光からの光）を導波光に変換する役割、または導波光を出力光（放射光）に変換する役割を果たす。
【００３２】
また、前記した本発明においては、導波層上には、導波層よりも低屈折率の第１の透明層が積層されており、第１の透明層上には強い光の照射によって不透明から透明に変化するマスク層や導波層の断絶位置を除いた位置で反射層が積層されていてもよい。前記において、強い光の照射によって不透明から透明に変化するマスク層とは、たとえば厚さ数十ｎｍ程度のアンチモン薄膜からなるマスクである。また強い光とは、たとえば数ｍＷ／μｍ² を越える光強度をいう。
【００３３】
また、導波層の断絶位置において断絶部が導波層よりも高屈折率の第２の透明層で覆われており、断絶部の形状が光軸を中心軸とする円錐状または円錐台状としてもよい。また、前記のマスク層が第１の透明層上でなく、第２の透明層上にあってもよい。
【００３４】
透明基板上又はその近傍には光検出器が形成され、断絶位置において導波層から信号面側に漏れ出て信号面を反射する光や、導波層に帰還して周期構造の中心から外周側に伝搬する導波光を光検出器で検出することで、信号面上に形成された信号や信号面上の凹凸構造を識別する。
【００３５】
導波層は多層膜で構成され、導波層内を伝搬する導波光の等価屈折率がＴＥモードとＴＭモードとでほぼ等しくなることを特徴とする。例えば導波層を構成する多層膜が、低屈折率の透明層の間に高屈折率の透明層を挟んだ３層構造で形成され、または高屈折率の透明層の間に低屈折率の透明層を挟んだ３層構造で形成される。
【００３６】
円錐体底面上又はその近傍には光検出器が形成され、断絶位置において導波層から信号面側に漏れ出て信号面を反射する光や、導波層に帰還して中心から外周側に伝搬する導波光を光検出器で検出することで、信号面上に形成された信号や信号面上の凹凸構造を識別する。
【００３７】
導波層は多層膜で構成され、導波層内を伝搬する導波光の等価屈折率がＴＥモードとＴＭモードとでほぼ等しくなるように形成されていてもよい。例えば導波層を構成する多層膜が、低屈折率の透明層の間に高屈折率の透明層を挟んだ３層構造で形成され、または高屈折率の透明層の間に低屈折率の透明層を挟んだ３層構造で形成される。
【００３８】
【第１実施の形態】
以下本発明の第１実施の形態を、図１から図３に基づいて説明する。図１は、本発明の第１実施の形態における情報記録再生装置の断面構造を示す。
【００３９】
図１に於いて、半導体レーザー等の放射光源１が板バネ状の部材２の先端に設けられたホルダー３の内部に固定されている。この放射光源１からは、軸Ｌを光軸とする光４が放射される。ホルダー３には光軸Ｌに直交して、Ｓｉ基板や石英基板などの透明平行基板５（放射光４の波長が１．２μｍ以上の場合にはＳｉ基板も透明である）が固定されており、この基板の裏側表面には光検出器５Ｄが光軸Ｌとの交点Ｏを中心とする直径数十μｍ程度の円形領域に形成されており、これを取り巻く外周の領域には点Ｏを中心とする同心円状グレーティング５Ｇが形成されている。
【００４０】
基板５の表面には、ＳｉＯ₂ 等の低屈折率の透明層６を挟んで導波層７が成膜されている。透明層６の厚さは１μｍ程度なので、基板上のグレーティング５Ｇの凹凸形状が透明層６と導波層７との界面にも残って、グレーティング６Ｇを形成する。
【００４１】
導波層７上にはＳｉＯ₂ 等の低屈折率の透明層８を挟んで、Ｃｒなどの反射層９が成膜される。反射層９の光軸Ｌを中心とする微小な円形領域（例えば直径０．５μｍ以下）をエッチングにより抜いた後、下地の透明層８、導波層７をドライエッチング等の方法で抜いて、光軸Ｌを中心軸とする円錐台状の孔１０を形成する。さらに、反射層９上には、この円錐台孔１０を埋没させるようにＳｉ、ＩｎＰ、ＧａＡｓ等の、導波層７よりも高屈折率の透明層１１が積層され、円錐台部１０を形成する。
【００４２】
透明層１１の表面は高い平面性を確保するために研磨が必要であり、円錐台部１０の部分だけが残るまでの研磨を加えてもよい。透明層１１は、厚さδの空気層１２を挟んでディスク基板１３上に形成された信号膜１４に近接している。いわゆる磁気ディスクで見られるフライングヘッドの技術と同様に、板バネ２を介してホルダー３を高速回転しているディスク基板１３上に押しあてることで、一定の空気ギャップ（例えば５０ｎｍ以下のδ）を保ちながら、透明層１１表面を安定して信号膜１４に近接させることができる。
【００４３】
平行基板５に入射し透過する光４は、透明層６を経て導波層７に入射し、同心円状のグレーティング６Ｇにより、外周側から中心に向かう導波光１５を励起する。この励起条件は、グレーティング６ＧのピッチをΛ、導波光の等価屈折率をＮ、波長をλ、入射角をθとして、下記式（数１）で与えられる。
【００４４】
【数１】
sinθ＝λ／Λ−Ｎ（式１）
前記式１において、ピッチΛは入射角θ、すなわち半径ｒの関数である。
【００４５】
また、入射光のうち導波層７を透過する成分は、反射層９を反射して導波層７に再入射してその一部が結合するので、全体の入力効率は高まる。導波層７はグレーティング６Ｇの中心位置で断絶する上、この位置で導波層よりも高い屈折率の透明媒質で形成される円錐台部１０に接するので、断絶位置に到達する導波光１５は導波層７から円錐台部１０の内部に吸い寄せられて光軸Ｌの周りに集まる光１６となり、その一部が円錐台部１０の底面の開口部９Ａ（反射層９のエッチング部）を経て透明層１１表面からエバネッセント光１７として外部に漏れ出る。エバネッセント光１７が信号膜１４の表面に近接すると、信号膜１４へ光エネルギーが流出したり、信号膜１４からの反射光１８という形で光エネルギーが流入する。信号膜１４が光や熱により反射率の変化する材料で形成されている場合は、このエバネッセント光１７により信号膜１４上に周りと反射率の異なる信号マーク１９を記録できる。なお、上記実施例では反射層９を用いたが、この代わりに強い光の照射によって不透明から透明へ変化する膜（マスク層）を透明層８上の全面に形成してもよい。また、マスク層上を前記実施例の透明層１１上に形成してもよい。いずれの場合も、中心から離れた領域では導波光１５の光量が小さく、そのエバネッセント光も弱いのでマスク層は不透明で反射層の働きをする。中心近傍では導波光１５の光量が強まり、そのエバネッセント光も強いので、マスク層は透明になりエバネッセント光１７を外部に導き出すことができる。
【００４６】
また、信号膜１４の状態の変化は、エバネッセント光１７の流出量を変化させ、信号膜１４からの反射光１８の光量も変化させる。この光エネルギーの流出入条件の変化は光検出器５Ｄの近傍での光を散乱させ、この散乱光が検出される。従って光検出器５Ｄにより信号マーク１９を検出することができ、閉じた空間内での光検出なので検出感度も高い。
【００４７】
図２Ｂは、本発明の第１実施の形態における、光利用効率を説明するための光強度分布図である。図２Ａは、グレーティング６Ｇを光源側から見た図で、グレーティング６Ｇの各位置に入射する光はそれぞれ外周から中心に向かう導波光１５（１５Ｅ，１５Ｍ等）を励起する。
【００４８】
入射光の導波光への変換効率（入射光量に対する中心位置での導波光量の比）は実験では２６％を越えており、反射層９での反射による入力効果も含めると、４０％以上の効率が見込める。これだけ高い効率が得られるのは、グレーティング６Ｇのピッチが位相整合条件（式１）を満たすので、入力した導波光が次のポイントに伝搬したときの位相と、そのポイントで入力した導波光の位相とが整合し、伝搬に伴って導波光量を増幅させるためである。この効果に加えて、外周側から中心に向かう収束性の伝搬であるので、導波光１５は中心に近づくごとにその光強度を増大さす。
【００４９】
図２Ｂには、中心を通る断面での導波光強度の分布を示す。最も光エネルギーが集中する中心位置(ｒ＝０)での導波光のうち、エバネッセント光１７として取り出せるのは約１０〜２０％程度と考えられるので、全体として１０^-2〜１０^-1程度の光利用効率が得られ、これは従来例と比べ千倍から万倍以上の高い効率である。また、第１実施の形態ではエバネッセント光放出部の構造が面的な広がりをなすので、熱集中が起こりにくく熱損傷に強い効果も合わせ持つ。
【００５０】
図３Ａは、本発明の第１実施の形態における光検出器と、図３Ｂは、信号面の構成図を光源側から見て示している。信号面には、凸部２０Ｇと凹部２０Ｌとによる凹凸状の溝が形成されており、凸部２０Ｇが透明層１１表面と近接している。エバネッセント光放出部の位置１７ａは凸部２０Ｇの中心に位置しており
、この位置１７ａはディスク基板１３の回転によって、図３Ｂに示す矢印２１Ｓの方向に移動する。
光検出器５Ｄは、中心Ｏを通り信号面上の溝と平行な線およびこれに直交する線で５Ｄａ，５Ｄｂ，５Ｄｃ，５Ｄｄに４等分割されている。各分割された検出器からはＡｌ等の金属膜によりパッド２２ａ、２２ｂ，２２ｃ、２２ｄへ配線されており、これらのパッドから外部へ検出信号が手渡される。
【００５１】
光検出器５Ｄの検出光量は、エバネッセント光放出部の位置１７ａと信号マーク１９の位置関係で決まり、位置１７ａが信号マーク１９ａや１９ｂの上を通過することで、５Ｄａ，５Ｄｂ，５Ｄｃ，５Ｄｄから出力される検出光量の総和が変化し、これを信号マークの再生信号とすることができる。また信号マークの位置により光検出器５Ｄへ入射する光の分布が変化することを利用して、（５Ｄａ＋５Ｄｂ）−（５Ｄｃ＋５Ｄｄ）を再生信号としてもよい。同様に光検出器５Ｄへの入射光の分布は、エバネッセント光の位置１７ａが矢印２１Ｔ方向に変位しても変化するので、（５Ｄａ＋５Ｄｄ）−（５Ｄｂ＋５Ｄｃ）を溝２０Ｇに対するトラッキング誤差信号とすることができる。
【００５２】
なお入射光４の偏光状態を直線偏光とし、その電気ベクトルが図２Ａの矢印４Ｅの方向を向いているものとすると、矢印４Ｅに直交する方向１５ＥにはＴＥモードが励起され、平行な方向１５ＭにはＴＭモードが励起され、それらの間の方向には両者が混在して励起される。
【００５３】
導波光の等価屈折率Ｎは導波モードによって異なり、一般にＴＥモード（導波光の電気ベクトルが導波面に平行な導波モード）の等価屈折率は、ＴＭモード（導波光の電気ベクトルが導波面に非平行な導波モード）の等価屈折率より大きい。従って、導波光の等価屈折率ＮがＴＥモードの等価屈折率に等しい時には１５Ｍ方向の導波光励起がなく、ＴＭモードの等価屈折率に等しい時に１５Ｅ方向の導波光励起がない。もし光入力効率を増大させるため全方位にわたって導波光を励起させるには、ＴＥモードとＴＭモードの等価屈折率を等しくさせることが好ましい。
【００５４】
【第２実施の形態】
図４Ａは、本発明の第２実施の形態における導波層の断面構造と、図４Ｂは、同導波層の等価屈折率を示した説明図であり、本実施の形態に限り光源の波長を０．７８μｍとしている。第２実施の形態は、導波層７の構成以外は全て第１実施の形態と同一であり、同一部の説明を省略する。
【００５５】
図４Ａにおいて、導波層７は２．１０の高屈折率の膜を１．７５の低屈折率の膜で挟み込んだ３層構造をなす。屈折率２．１０の膜は例えばＴａ₂Ｏ₅をターゲットとしてスパッタにより成膜できる。屈折率１．７５の膜は、例えばＴａ₂Ｏ₅とＳｉＯ₂との混合ターゲットをスパッタすることにより成膜できる。
【００５６】
図４Ｂにおいて、縦軸は等価屈折率、横軸は屈折率２．１０の膜の厚さｄをとっており、透明層６及び８の屈折率を１．４５、屈折率１．７５の膜の厚さを上下とも０．２２３μｍとしている。ｄ＝０．１６μｍの時、ＴＥ１とＴＭ１とで等価屈折率が一致し（Ａ点参照）、ＴＥ１の曲線とＴＭ１の曲線が漸近する形で接するのでｄの誤差に対しても裕度がある。従って、本発明の第２実施の形態により、ＴＥモードとＴＭモードの等価屈折率を等しくさせることが可能となり
、第１実施の形態よりもさらに光利用効率を増大させることができる。
【００５７】
なお、低屈折率の膜を高屈折率の膜で挟み込んだ３層構造の導波層であってもよい。
【００５８】
【第３実施の形態】
次に本発明の第３実施の形態を、図５と図６Ａ及び図６Ｂを用いて説明する。図５は本発明の第３実施の形態における情報記録再生装置の断面構成を示している。第３実施の形態は第１実施の形態と比べて、グレーティングと光検出器の構成が変わるだけで、その他の構成については全く同じであり、同一部については説明を省略する。
【００５９】
図５に於いて、光検出器５Ｄが形成された透明平行基板５の表面には、ＳｉＯ２等の低屈折率の透明層６が形成され、光軸Ｌとの交点Ｏを中心とする同心円状のグレーティング６Ｇが、透明層６表面の点Ｏを取り巻く輪帯領域に形成されている。透明層６上には導波層７が成膜され、反射層９等その他の構成については第１実施の形態と同じである。
【００６０】
平行基板５に入射し透過する光４は、光検出器５Ｄが形成されている側では遮光されるが、形成されていない側では透明層６を経て導波層７に入射し、同心円状のグレーティング６Ｇにより、外周側から中心Ｏに向かう導波光１５を励起する。また入射光のうち導波層７を透過する成分は、反射層９を反射して導波層７に再入射してその一部が結合するので、全体の入力効率は高まる。
【００６１】
導波層７は、グレーティング６Ｇの中心位置で断絶する上、この位置で導波層よりも高い屈折率の透明媒質で形成される円錐台部１０に接するので、断絶位置に到達する導波光１５は導波層７から円錐台部１０の内部に吸い寄せられて、光軸Ｌの周りに集まる光１６となり、その一部が円錐台部１０の底面の開口部９Ａ（反射層９のエッチング部）を経て、透明層１１表面からエバネッセント光１７として外部に漏れ出る。
【００６２】
エバネッセント光１７が信号膜１４の表面に近接すると、信号膜１４へ光エネルギーが流出したり、信号膜１４からの反射光１８という形で光エネルギーが流入する。
【００６３】
信号膜１４が光や熱により反射率の変化する材料で形成されている場合は、このエバネッセント光１７により信号膜１４上に周りと反射率の異なる信号マーク１９を記録できる。また信号膜１４の状態の変化は、エバネッセント光１７の流出量を変化させ、信号膜１４からの反射光１８の光量も変化させる。この光エネルギーの流出入条件の変化は、断絶位置をすり抜け中心から外周側に向かう導波光１５Ａ（以下、帰還導波光と呼ぶ）の強度を変化させ、グレーティング６Ｇにより検出器５Ｄ側に放射する光１５Ｂの強度も変化する。従って光検出器５Ｄにより信号マーク１９を検出することができる。なお、上記実施例では反射層９を用いたが、この代わりに強い光の照射によって不透明から透明へ変化する膜（マスク層）を透明層８上の全面に形成してもよい。また、マスク層上を前記実施例の透明層１１上に形成してもよい。いずれの場合も、中心から離れた領域では導波光１５の光量が小さく、そのエバネッセント光も弱いのでマスク層は不透明で反射層の働きをする。中心近傍では導波光１５の光量が強まり、そのエバネッセント光も強いので、マスク層は透明になりエバネッセント光１７を外部に導き出すことができる。
【００６４】
図６Ａは、本発明の第３実施の形態における情報記録再生装置の光検出器を示し、図６Ｂは、信号面の構成図を光源側から見て示している。図６Ｂにおいて、ディスク基板１３上の信号面には、凸部２０Ｇと凹部２０Ｌによる凹凸状の溝が形成されており、凸部２０Ｇが透明層１１表面と近接している。透明層１１表面からのエバネッセント光放出部の位置１７ａは凸部２０Ｇの中心に位置しており、この位置１７ａはディスク基板１３の回転によって矢印２１Ｓの方向に移動する。
【００６５】
光検出器の形成される領域は図６Ａに示したように、中心Ｏを通る直線で等分割された６つの扇形のうち一つおきに配置された３つの扇形（５Ｄａ、５Ｄｂ、５Ｄｃ）上に限られ、各検出器からはＡｌ等の金属膜によりパッド２２ａ、２２ｂ，２２ｃへ配線されており、これらのパッドから外部へ検出信号が手渡される。光検出器の領域では入射光４が遮られるので、グレーティング６Ｇによる導波光の励起は、残された３つの扇形の領域で１５ａ，１５ｂ，１５ｃの如くなされる。
【００６６】
断絶部で導波層７から漏れ出ずに通過する導波光や信号面を反射して導波層７に取り込まれる帰還導波光は、中心位置Ｏを通過した後その位置でのグレーティング６Ｇにより光検出器５Ｄａ、５Ｄｂ、５Ｄｃに放射される。これらの放射光量、すなわち光検出器での検出光量は、エバネッセント光１７と信号マーク１９との位置関係で決まり、位置１７ａが信号マーク１９ａや１９ｂの上を通過することで、５Ｄａ，５Ｄｂ，５Ｄｃで検出される光量の総和が変化し、これを信号マークの再生信号とすることができる。また検出器の分割線の一つが矢印２１Ｓに直交するとして、信号マークの位置により帰還導波光の分布が変化することを利用して、５Ｄａ＋５Ｄｂ−５Ｄｃを再生信号としてもよい。同様に帰還導波光の分布はエバネッセント光の位置１７ａが矢印２１Ｔ方向に変位しても変化するので、５Ｄａ−５Ｄｂをトラッキング誤差信号とすることができる。
【００６７】
なお、第３実施の形態については、図６Ａに示す光検出器の形状に他の形態も考えられ、例えば中心Ｏを通る直線で等分割された１０個の扇形のうち一つおきに配置された５つの扇形であっても同様の効果が得られる。
【００６８】
第３実施の形態は、光検出器の形成された扇領域と導波光が励起される扇領域が分離しているので、第１実施の形態のように中心に向かう導波光からの散乱光が光検出器に入射して検出されることがなく、往路に於ける伝搬方向から偏向して外周側に向かう帰還導波光だけを検出できるので、第１実施の形態と比べて高品質の信号再生が可能である。
【００６９】
【第４実施の形態】
図７Ａは、本発明の第４実施の形態における情報記録再生装置の光検出器を示し、図７Ｂは、信号面の構成図を光源側から見て示している。第４実施の形態は、第３実施の形態と比べて光検出器の構成が変わるだけで、その他の構成については全く同じであり、断面構成図は第３実施の形態で示した図５を使い、同一部については説明を省略する。図７Ｂにおいて、ディスク基板１３上の信号面には凸部２０Ｇと凹部２０Ｌによる凹凸状の溝が形成されており、凸部２０Ｇが透明層１１表面と近接している。透明層１１表面からのエバネッセント光放出部の位置１７ａは凸部２０Ｇの中心に位置しており、この位置１７ａはディスク基板１３の回転によって矢印２１Ｓの方向に移動する。
【００７０】
光検出器の形成される領域は、中心Ｏを通る直線で等分割された８つの扇形のうち一つおきに配置された４つの扇形（５Ｄａ、５Ｄｂ、５Ｄｃ、５Ｄｄ）上に限られ、各検出器からはＡｌ等の金属膜によりパッド２２ａ、２２ｂ，２２ｃ，２２ｄへ配線されており、これらのパッドから外部へ検出信号が手渡される。光検出器の領域では入射光４が遮られるので、グレーティング６Ｇによる導波光の励起は残された４つの扇形の領域で１５ａ，１５ｂの如くなされる。
【００７１】
断絶部で導波層７から漏れ出た後、信号面を反射して導波層７に取り込まれる導波光（帰還導波光）は、中心位置Ｏを通過したのち外周側に向かう。特に光検出器５Ｄａ、５Ｄｂ、５Ｄｃ、５Ｄｄの方位に伝搬する帰還導波光は、その位置でのグレーティング６Ｇにより光検出器に放射される。帰還導波光の伝搬方位は、エバネッセント光１７と信号マーク１９の位置関係により変化するので、位置１７ａが信号マーク１９ａや１９ｂの上を通過することで、５Ｄａ，５Ｄｂ，５Ｄｃ、５Ｄｄで検出される光量の総和が変化し、これを信号マークの再生信号とすることができる。また５Ｄｃ、５Ｄｄの対称線が矢印２１Ｓの方位に並んだ位置関係であれば、信号マークの位置により帰還導波光の伝搬方位が変化することを利用して、５Ｄａ−５Ｄｂを再生信号としてもよい。同様に帰還導波光の伝搬方位はエバネッセント光の位置１７ａが矢印２１Ｔ方向に変位しても変化するので、５Ｄｃ−５Ｄｄをトラッキング誤差信号とすることができる。
【００７２】
なお、第４実施の形態については、図７Ａに示す光検出器の形状に他の形態も考えられ、例えば中心Ｏを通る直線で等分割された１２つの扇形のうち一つおきに配置された６つの扇形であっても同様の効果が得られる。第４実施の形態は、帰還導波光のうち伝搬方位の変化したもの（すなわち信号マークの影響をうけた成分）だけを検出するので、第３実施の形態と比べても高品質の信号再生が可能である。
【００７３】
【第５実施の形態】
図８は、本発明の第５実施の形態における情報記録再生装置の断面構成を示す。第５実施の形態は、第１実施の形態と比べて光結合手段の構成が変わるだけで、その他の構成については全く同じであり、同一部については説明を省略する。図８に於いて、半導体レーザー等の放射光源１が、板バネ上の部材２の先端に設けられたホルダー３の内部に固定されている。この放射光源１からは、軸Ｌを光軸とする光４が放射される。ホルダー３には光軸Ｌと同軸してコリメートレンズ２３と円錐レンズ２４とが取り付けられている。
【００７４】
円錐レンズ２４の屈折率は、後述する導波層７の屈折率よりも高く、その底面には、光検出器５Ｄが光軸Ｌとの交点Ｏを中心とする直径数十μｍ程度の円形領域に形成されている。円錐レンズの低面には、ＳｉＯ₂ 等の低屈折率の透明層６を挟んで導波層７が成膜され、その他の構成は第１実施の形態と同じなので説明を省略する。
【００７５】
コリメートレンズ２３により平行光４ａとなった光は、円錐レンズ２４の円錐面を屈折して円錐状の波面をなす光４ｂとなり、透明層６を経て導波層７に入射し、透明層６が十分薄い場合に外周側から中心に向かう導波光１５を励起する。この励起条件は円錐レンズ２４の屈折率をｎ、導波光の等価屈折率をＮ、入射角をθとして、下記式（数２）で与えられる。
【００７６】
【数２】
ｎsinθ＝Ｎ（式２）
第５実施の形態は、光を導波層に入力する光結合手段が第１実施の形態と異なるだけで、第１実施の形態でグレーティング６Ｇであったものが、第５実施の形態では円錐状のレンズ２４に変わるだけである。従って第１実施の形態と同様に信号面上に信号を記録したり、再生したりでき、グレーティングによる光入力よりもプリズム（円錐レンズ）による光入力が一般に高効率であるので、第１実施の形態よりも高い光利用効率が得られる。
【００７７】
また、第１実施の形態と同様にエバネッセント光放出部の構造が面的な広がりをなすので、熱損傷に強い効果も合わせ持つ。当然、第１実施の形態と同じく反射層９の代わりにマスク層を用いてもよく、マスク層を透明層１１上に形成してもよい。さらに第２実施の形態で示した３層の導波層や第３、第４実施の形態で示した検出方式を採用することもでき、全く同様の効果が得られる。反対に第１実施の形態から第４実施の形態においては、第５実施の形態のようにコリメーターレンズで光を平行にしてグレーティングに入射する方式でもよい。
【００７８】
なお、信号の検出方法には光源への帰還光量の増減に伴う発光特性の変化を利用する方法もあり、この場合第１実施の形態から第５実施の形態において検出器５Ｄは不要であり、替わりに光源の発光特性（半導体レーザーの場合には駆動電流値の変動）をモニターすることで帰還光量の大小、すなわち信号の有無を判定できる。
【００７９】
また、等方的な光入力結合を果たすため、１／４波長板で光源の光を円偏光に変換して導波層に入力することも考えられ、工程を削減するために反射層９の形成を省いてもよく、グレーティング６Ｇは導波層表面に形成されてもよい。
【００８０】
また、導波層の断絶部は、外周側から中心に伝搬する導波光を信号面側に漏れ出させる機能さえあれば、上記実施の形態であげた以外の形態も考えられ、例えば円錐台部１０の形状は信号面側の方に狭まる形状でもよく、円錐台部を埋める媒質に導波層よりも低屈折率の材料を用いてもよい。
【００８１】
また、信号面には光磁気ディスクで用いられている膜で形成されてもよい。さらに、本発明の各実施の形態での構成を入れ替えたものであってもよい。
なお、第１実施の形態から第５実施の形態において、平面上に導波層を形成したもので説明をしたが、曲面上であってもよく、例えば円錐面上に導波層を形成し、円錐の頂点位置に断絶部を設けてもよい。
【００８２】
【発明の効果】
前記した本発明によれば、高効率に導波光を発生させる一方、導波モードに準じた状態で光を低損失に伝搬させながら集中させることができ、高屈折率の円錐台部の存在により高エネルギーの光をエバネッセント光として信号面上に効果的に導き出すさせることができるので光利用効率を大幅に向上させることができ、高い情報転送速度を維持したまま光の回折限界を超えた高密度の情報記録再生が可能となる。
【００８３】
また、押圧力の加わった状態での信号面との相対移動により、導波層表面が信号面との近接位置を保ったまま安定的に浮上走査でき、導波層近傍に設けられた検出手段により、信号面からの反射光や導波層内を中心から外周側に伝搬する導波光等の光量を効率よく検出できるので、信号の再生感度を大幅に高められ、差分検出により信号面上のトラックを認識できる。
【００８４】
また、エバネッセント光放出部の構造が面的な広がりをなすので熱集中が起こりにくく熱損傷による劣化がなく、空気層を挟んだ浮上走査方式によりエバネッセント光放出部を信号面に近接させながら安定に走査させることが可能で、装置としての構成が容易である。
【００８５】
さらに、エバネッセント光の流出条件の変化や反射光、帰還導波光の光量変化を導波層に近接した検出器で検知することができるので、信号再生感度を大幅に高めるとともに、エバネッセント光放出部の位置の変化が反射光、帰還導波光の分布や伝搬方位に影響することから検出信号の差分により信号面上の信号マークやトラックを認識できる、などの効果がある。
【図面の簡単な説明】
【図１】本発明の第１実施の形態における情報記録再生装置の断面構成図である。
【図２】Ａは本発明の第１実施の形態におけるグレーティングの平面図であり、Ｂは同グレーティングの光利用効率を説明する光強度分布図である。
【図３】Ａは本発明の第１実施の形態における光検出器の要部平面図であり、Ｂは信号面の構成平面図である。
【図４】Ａは本発明の第２実施の形態における導波層の断面構成図であり、Ｂは同導波層を用いた等価屈折率を示した説明図である。
【図５】本発明の第３実施の形態における情報記録再生装置の断面構成図である。
【図６】Ａは本発明の第３実施の形態における情報記録再生装置の光検出器の要部平面図であり、Ｂは信号面の構成平面図である。
【図７】Ａは本発明の第４実施の形態における情報記録再生装置の光検出器の要部平面図であり、Ｂは信号面の構成平面図である。
【図８】本発明の第５実施の形態における情報記録再生装置の断面構成図である。
【図９】従来の情報記録再生装置の断面構成図である。
【図１０】Ａは従来の情報記録再生装置の要部断面図であり、Ｂは同装置における光伝搬方向に沿った光エネルギー分布図である。
【符号の説明】
１放射光源
２板バネ
３ホルダー
４放射光
Ｌ光軸
５透明平行基板
５Ｄ光検出器
５Ｇグレーティング
６透明層
６Ｇグレーティング
７導波層
８透明層
９反射層
１０円錐台部
１１透明層
１２空気層
１３ディスク基板
１４信号膜
１５導波光
１６集中光
１７エバネッセント光
１８反射光
１９信号マーク[0001]
BACKGROUND OF THE INVENTION
The present invention provides a device for recording or reproducing high-density information. In place It is related.
[0002]
[Prior art]
The conventional technology is described in, for example, J.Vac.Sci.technol.B13 (1995) 2813 by S.Hosaka, which is called SNOM (Scanning Near-Field Optical Microscope). Description will be made based on the information recording / reproducing apparatus. FIG. 9 is a sectional view of a conventional information recording / reproducing apparatus. An optical fiber composed of a high-refractive index core 25 and a low-refractive index cladding 26 surrounding the core 25 is cut into a conical shape, and a cladding 26 and a reflective film 27 are formed so as to surround the core. Has been. The tip of this conical portion faces the recording film 14 formed on the disk substrate 13 with a slight gap δ.
[0003]
The gap δ is a minute amount of 50 nm or less, and the core diameter of the cone tip is about 0.1 μm. When the light from the radiation source is input to the optical fiber, the evanescent light 29 oozes from the tip of the cone. Since the tip of the cone is close to the recording film 14, for example, if the recording film 14 is a phase change film, the signal mark 19 having a different reflectance from the surroundings is formed on the recording film by the thermal energy of the evanescent light 29. it can. Further, the presence or absence of the signal mark 19 can be determined by detecting the reflected / scattered light 30 from the recording film 14 with the photodetector 31.
[0004]
The above information recording / reproducing apparatus enables signal recording and signal reproduction corresponding to the core diameter of the cone tip. For example, when the diameter of the signal mark 19 is 0.1 μm, a digital video disc (hereinafter referred to as DVD) (signal) Compared with a mark diameter of about 0.3 to 0.4 μm, a high-density information recording / reproducing apparatus can be provided.
[0005]
Such a conventional information recording / reproducing apparatus has problems as shown in FIGS. 10A and 10B, for example. FIG. 10A shows a main part of a conventional information recording / reproducing apparatus, and FIG. 10B shows a light energy distribution diagram along the light propagation direction (−z axis) of the apparatus.
[0006]
In FIG. 10A, the guided light 28 propagating through the optical fiber propagates almost without loss (z> a) up to the front of the cone, but the incident light 28a is reflected from the refracted light 28b at the cone (a>z> 0). The light 28c is divided into the reflected light 28c again, and the above is repeated over and over the length a of the cone, so that the evanescent light 29 emitted from the tip of the cone is extremely become weak.
[0007]
In general, assuming that the optical energy of the guided light in front of the cone is 1, the optical energy η of the evanescent light 29 emitted from the tip of the cone is 10 ^-7 -10 ^-Five For example, the light utilization efficiency is extremely low as shown in FIG. 10B. Therefore, it takes a long time to record the recording film 14, and using it as an information recording apparatus sacrifices the significant reduction in information transfer speed while increasing the recording density.
[0008]
In addition, the tip (head) of the conical portion is like a point floating in a space, so that heat concentration easily occurs and deterioration due to heat damage easily occurs. Further, in order to stably scan the head close to the recording surface 14, a complicated mechanism is required and it is difficult to increase the density in the track direction because the track on the recording surface cannot be recognized.
[0009]
Further, the reproduction principle using the reflected scattered light 30 detects a very small part of the reflected scattered light having a wide spatial spread, and therefore the reproduction sensitivity is extremely poor.
[0010]
[Problems to be solved by the invention]
In view of such problems, the present invention greatly improves the light utilization efficiency, does not deteriorate due to thermal damage, can be stably scanned while the head is close to the signal surface, and recognizes the track on the signal surface. Control the signal reproduction sensitivity significantly. Feeling It is an object to provide an information recording / reproducing apparatus.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the first of the present invention Love The information recording / reproducing apparatus includes a radiation light source, a transparent substrate, a waveguide layer formed on a surface opposite to the light source of the transparent substrate, and an optical axis formed on the interface of the waveguide layer. The waveguide layer is cut off at the center position of the periodic structure, and the light from the radiation source is centered in the waveguide layer from the outer peripheral side of the periodic structure by the optical coupling means. The waveguide light propagating to the substrate is excited, and the guided light leaks to the signal surface on the flat substrate placed close to the waveguide layer at the break position of the waveguide layer.
[0012]
With this structure, the transparent substrate is fixed on the same structure as the radiation light source, and this structure can move relatively while being pressed against the signal surface by the pressing means.
Next, the second of the present invention Love The information recording / reproducing apparatus includes a radiation light source, a condensing unit that converts light emitted from the radiation light source into parallel light, a transparent cone having an optical axis of the parallel light as a central axis, and a lower surface portion of the cone A transparent buffer layer formed on the buffer layer and a waveguide layer formed on the buffer layer. The waveguide layer is cut off at a central axis position of the cone, and the refractive index of the cone and the waveguide are The refractive index of the layer and the refractive index of the buffer layer have a decreasing relationship in this order, and the parallel light is refracted on the conical surface of the cone and enters the waveguide layer through the buffer layer, so In the wave layer, the guided light propagating from the outer peripheral side to the central axis side is excited, and the guided light leaks to the signal surface on the flat substrate placed in the proximity of the waveguide layer at the cut-off position. It is characterized by exiting.
[0013]
With this structure, the cone is fixed on the same structure as the radiation light source and the light collecting means, and this structure can move relatively while being pressed against the signal surface by the pressing means.
[0014]
First of the present invention described above Love In the information recording / reproducing apparatus, the transparent substrate is fixed on the same structure as the radiation light source, and the structure is moved relatively while being pressed against the signal surface by a pressing means. It is preferable that the structure floats across the air layer while the surface of the layer faces the signal surface.
[0015]
Second of the present invention described above Love In the information recording / reproducing apparatus, the cone is fixed on the same structure as the radiation light source and the light collecting means, and the structure moves relatively while being pressed against the signal surface by the pressing means, It is preferable that the structure floats across the air layer while the waveguide layer surface faces the signal surface by this movement.
[0016]
Also, the first and second aspects of the present invention described above Love In the information recording / reproducing apparatus, it is preferable that a first transparent layer having a lower refractive index than that of the waveguide layer is laminated on the waveguide layer.
[0017]
Moreover, in the said apparatus, it is preferable that the reflection layer is laminated | stacked on the said 1st transparent layer in the position except the said disconnection position.
In the device, it is preferable that a mask layer that changes from opaque to transparent by irradiation with intense light is laminated on the first transparent layer.
[0018]
In the device, at the disconnection position, the disconnection portion is covered with a second transparent layer having a refractive index higher than that of the waveguide layer, and the guide in the waveguide layer is interposed via the second transparent layer. It is preferable that wave light leaks to the signal surface side.
[0019]
In the apparatus, it is preferable that a mask layer that changes from opaque to transparent by irradiation with intense light is laminated on the second transparent layer.
Moreover, in the said apparatus, it is preferable that the shape of the said interruption | blocking part is at least 1 shape determined from the cone shape centering on the said optical axis, and a truncated cone shape.
[0020]
In the apparatus, it is preferable that a signal mark is recorded on the signal surface by light leaking from the waveguide layer to the signal surface side at the disconnection position. Further, in the device, a photodetector is formed on or near the transparent substrate, and light leaking from the waveguide layer to the signal surface side at the disconnection position reflects the signal surface. It is preferable that a part of the signal is detected by the photodetector and the signal formed on the signal surface is reproduced.
[0021]
In the apparatus, it is preferable that the photodetector is equally divided by a dividing line orthogonal to the moving direction of the signal surface, and a difference signal between the equal divisions is used as a reproduction signal.
[0022]
Further, in the apparatus, a concavo-convex structure along the moving direction of the signal surface is formed on the signal surface, and the photodetector is equally divided by a dividing line along the moving direction. The difference signal between the divisions is preferably a tracking control signal.
[0023]
In the device, a photodetector is formed on or in the vicinity of the transparent substrate, and light leaking from the waveguide layer to the signal surface side at the cut-off position reflects the signal surface and again guides the wave. The light is taken into the layer and propagates in the waveguide layer from the center of the periodic structure to the outer peripheral side, and at least one of the waveguide light or the light emitted from the waveguide layer is detected by the detector. It is preferable to reproduce the signal formed on the signal surface.
[0024]
In the apparatus, the photodetector is preferably composed of two portions sandwiching a straight line orthogonal to the moving direction of the signal plane, and a difference signal between the two detectors is used as a reproduction signal.
[0025]
Further, in the apparatus, a concavo-convex structure is formed on the signal surface along the moving direction of the signal surface, and the photodetector is composed of two parts symmetrical with respect to a straight line along the moving direction, The difference signal between the two detectors is preferably used as a tracking control signal.
[0026]
In the device, light leaking from the waveguide layer to the signal surface side at the disconnection position reflects off the signal surface and is again taken into the waveguide layer, and the waveguide layer has a periodic structure. The guided light propagates from the center to the outer peripheral side, the guided light is fed back to the radiation light source again, the change in the driving characteristics of the radiation light source generated by this feedback is detected, and the signal formed on the signal surface is It is preferable to regenerate.
[0027]
In the device, it is preferable that the waveguide layer is formed of a multilayer film, and the equivalent refractive index of guided light propagating in the waveguide layer is substantially equal between the TE mode and the TM mode.
[0028]
In the device, the multilayer film constituting the waveguide layer is preferably formed in a three-layer structure in which a transparent layer having a high refractive index is sandwiched between transparent layers having a low refractive index.
In the above device, the multilayer film constituting the waveguide layer is preferably formed in a three-layer structure in which a transparent layer having a low refractive index is sandwiched between transparent layers having a high refractive index.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention described above, the generation of guided light by external input is limited to satisfying the resonance condition (input condition). When this condition is satisfied, part of the input light (light from the emitted light) is guided light. Is converted to This is called “excitation”.
[0030]
In addition, since a part of the input light (light from the radiated light) is converted into guided light, the integral of the guided light converted from the incident light on the outer peripheral surface becomes the guided light on the inner peripheral side. As a matter of course, input light is converted into guided light at an arbitrary position where it is currently guided, and is added to the guided light that has been propagated.
[0031]
In the present invention described above, the “optical coupling means” plays a role of converting input light (light from the emitted light) into guided light, or a role of converting the guided light into output light (radiated light).
[0032]
In the above-described present invention, the first transparent layer having a lower refractive index than that of the waveguide layer is laminated on the waveguide layer, and the first transparent layer becomes opaque by irradiation with strong light. The reflective layer may be laminated at a position other than the break position of the mask layer or waveguide layer that changes from transparent to transparent. In the above, the mask layer that changes from opaque to transparent by irradiation with strong light is a mask made of an antimony thin film having a thickness of, for example, about several tens of nanometers. The strong light is, for example, several mW / μm ² The light intensity exceeding.
[0033]
Further, the break portion is covered with a second transparent layer having a higher refractive index than the waveguide layer at the break position of the waveguide layer, and the shape of the break portion is a conical shape or a truncated cone shape having the optical axis as the central axis. It is good. The mask layer may be on the second transparent layer instead of on the first transparent layer.
[0034]
A photodetector is formed on or in the vicinity of the transparent substrate, and light that leaks from the waveguide layer to the signal surface side at the break position and reflects the signal surface, or returns from the center of the periodic structure to the waveguide layer. By detecting the guided light propagating to the side with a photodetector, the signal formed on the signal surface and the concavo-convex structure on the signal surface are identified.
[0035]
The waveguide layer is formed of a multilayer film, and the equivalent refractive index of guided light propagating in the waveguide layer is substantially equal between the TE mode and the TM mode. For example, a multilayer film constituting the waveguide layer is formed in a three-layer structure in which a transparent layer having a high refractive index is sandwiched between transparent layers having a low refractive index, or a low refractive index is formed between transparent layers having a high refractive index. It is formed with a three-layer structure with a transparent layer interposed therebetween.
[0036]
A photodetector is formed on or near the bottom of the cone, and light that leaks from the waveguide layer to the signal surface side at the break position and reflects the signal surface, or returns to the waveguide layer from the center to the outer peripheral side. By detecting the propagating guided light with a photodetector, the signal formed on the signal surface and the uneven structure on the signal surface are identified.
[0037]
The waveguide layer may be formed of a multilayer film, and may be formed so that the equivalent refractive index of guided light propagating in the waveguide layer is substantially equal between the TE mode and the TM mode. For example, a multilayer film constituting the waveguide layer is formed in a three-layer structure in which a transparent layer having a high refractive index is sandwiched between transparent layers having a low refractive index, or a low refractive index is formed between transparent layers having a high refractive index. It is formed with a three-layer structure with a transparent layer interposed therebetween.
[0038]
[First embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a cross-sectional structure of an information recording / reproducing apparatus according to a first embodiment of the present invention.
[0039]
In FIG. 1, a radiation light source 1 such as a semiconductor laser is fixed inside a holder 3 provided at the tip of a plate spring-like member 2. The radiation light source 1 emits light 4 having an axis L as an optical axis. A transparent parallel substrate 5 such as a Si substrate or a quartz substrate (the Si substrate is also transparent when the wavelength of the emitted light 4 is 1.2 μm or more) is fixed to the holder 3 perpendicular to the optical axis L. On the back surface of the substrate, the photodetector 5D is formed in a circular area having a diameter of about several tens of μm centered on the intersection O with the optical axis L, and the point O is centered on the outer peripheral area surrounding this. The concentric grating 5G is formed.
[0040]
On the surface of the substrate 5, SiO ₂ A waveguide layer 7 is formed with a transparent layer 6 having a low refractive index interposed therebetween. Since the thickness of the transparent layer 6 is about 1 μm, the uneven shape of the grating 5G on the substrate remains at the interface between the transparent layer 6 and the waveguide layer 7 to form the grating 6G.
[0041]
On the waveguide layer 7 is SiO. ₂ A reflective layer 9 such as Cr is formed with a transparent layer 8 having a low refractive index interposed therebetween. After removing a minute circular region (for example, a diameter of 0.5 μm or less) around the optical axis L of the reflective layer 9 by etching, the underlying transparent layer 8 and the waveguide layer 7 are removed by a method such as dry etching, A truncated cone-shaped hole 10 having the optical axis L as a central axis is formed. Further, a transparent layer 11 having a refractive index higher than that of the waveguiding layer 7 such as Si, InP, or GaAs is laminated on the reflective layer 9 so as to bury the truncated cone hole 10, thereby forming the truncated cone portion 10. To do.
[0042]
The surface of the transparent layer 11 needs to be polished to ensure high flatness, and polishing may be performed until only the portion of the truncated cone portion 10 remains. The transparent layer 11 is close to the signal film 14 formed on the disk substrate 13 with the air layer 12 having a thickness δ interposed therebetween. Similar to the flying head technology found in so-called magnetic disks, a fixed air gap (for example, δ of 50 nm or less) is obtained by pressing the holder 3 onto the disk substrate 13 rotating at high speed via the leaf spring 2. While maintaining, the surface of the transparent layer 11 can be brought close to the signal film 14 stably.
[0043]
The light 4 incident on and transmitted through the parallel substrate 5 enters the waveguide layer 7 through the transparent layer 6, and excites the waveguide light 15 from the outer peripheral side toward the center by the concentric grating 6G. This excitation condition is given by the following formula (Equation 1), where the pitch of the grating 6G is Λ, the equivalent refractive index of guided light is N, the wavelength is λ, and the incident angle is θ.
[0044]
[Expression 1]
sinθ = λ / Λ−N (Formula 1)
In Equation 1, the pitch Λ is a function of the incident angle θ, that is, the radius r.
[0045]
In addition, the component of the incident light that passes through the waveguiding layer 7 is reflected by the reflecting layer 9 and re-enters the waveguiding layer 7 to be partially coupled, so that the overall input efficiency is increased. Since the waveguide layer 7 is disconnected at the center position of the grating 6G, and is in contact with the truncated cone portion 10 formed of a transparent medium having a higher refractive index than the waveguide layer at this position, the guided light 15 reaching the disconnection position is Light 16 is attracted from the waveguide layer 7 to the inside of the truncated cone part 10 and gathers around the optical axis L, and a part of the light 16 passes through the opening 9A (the etched part of the reflective layer 9) on the bottom surface of the truncated cone part 10. It leaks to the outside as evanescent light 17 from the surface of the transparent layer 11. When the evanescent light 17 approaches the surface of the signal film 14, light energy flows out to the signal film 14 or light energy flows in the form of reflected light 18 from the signal film 14. When the signal film 14 is formed of a material whose reflectance changes due to light or heat, the signal mark 19 having a reflectance different from that of the surroundings can be recorded on the signal film 14 by the evanescent light 17. The Although the reflective layer 9 is used in the above embodiment, a film (mask layer) that changes from opaque to transparent by irradiation with strong light may be formed on the entire surface of the transparent layer 8 instead. Further, the mask layer may be formed on the transparent layer 11 of the above embodiment. In either case, the light quantity of the guided light 15 is small and the evanescent light is weak in a region away from the center, so that the mask layer is opaque and functions as a reflective layer. In the vicinity of the center, the light quantity of the guided light 15 is increased and the evanescent light is also strong, so that the mask layer becomes transparent and the evanescent light 17 can be led out.
[0046]
Moreover, the change in the state of the signal film 14 changes the outflow amount of the evanescent light 17 and also changes the amount of the reflected light 18 from the signal film 14. This change in the inflow / outflow conditions of light energy scatters light in the vicinity of the photodetector 5D, and this scattered light is detected. Therefore, the signal mark 19 can be detected by the photodetector 5D, and the detection sensitivity is high because the light is detected in a closed space.
[0047]
FIG. 2B is a light intensity distribution diagram for explaining light utilization efficiency in the first embodiment of the present invention. FIG. 2A is a view of the grating 6G as viewed from the light source side. Light incident on each position of the grating 6G excites the guided light 15 (15E, 15M, etc.) from the outer periphery toward the center.
[0048]
The conversion efficiency of incident light into guided light (ratio of the amount of guided light at the center position with respect to the amount of incident light) exceeds 26% in the experiment, and including the input effect due to reflection at the reflective layer 9, it is 40% or more. Efficiency can be expected. This high efficiency is obtained because the pitch of the grating 6G satisfies the phase matching condition (Equation 1), so the phase when the input guided light propagates to the next point and the phase of the guided light input at that point Is matched, and the amount of guided light is amplified along with propagation. In addition to this effect, since the propagation is convergent from the outer peripheral side toward the center, the light intensity of the guided light 15 increases as it approaches the center.
[0049]
FIG. 2B shows a distribution of guided light intensity in a cross section passing through the center. Of the guided light at the center position (r = 0) where the light energy is most concentrated, it is considered that about 10 to 20% can be extracted as the evanescent light 17, so that 10% as a whole. ^-2 -10 ^-1 A light utilization efficiency of about a degree is obtained, which is a high efficiency that is 1,000 to 10,000 times that of the conventional example. Further, in the first embodiment, the structure of the evanescent light emitting portion is spread over the surface, so that heat concentration is difficult to occur and it has a strong effect on thermal damage.
[0050]
FIG. 3A shows the photodetector in the first embodiment of the present invention, and FIG. 3B shows a configuration diagram of the signal surface as viewed from the light source side. On the signal surface, a concavo-convex groove is formed by the convex portion 20G and the concave portion 20L, and the convex portion 20G is close to the surface of the transparent layer 11. The position 17a of the evanescent light emitting part is located at the center of the convex part 20G.
The position 17a is moved in the direction of the arrow 21S shown in FIG.
The photodetector 5D is divided into four equal parts of 5Da, 5Db, 5Dc, and 5Dd by a line passing through the center O and parallel to the groove on the signal surface and a line orthogonal thereto. Each divided detector is wired to pads 22a, 22b, 22c and 22d by a metal film such as Al, and a detection signal is handed to the outside from these pads.
[0051]
The amount of light detected by the photodetector 5D is determined by the positional relationship between the position 17a of the evanescent light emitting portion and the signal mark 19, and when the position 17a passes over the signal marks 19a and 19b, from 5Da, 5Db, 5Dc, and 5Dd The sum of the detected light amounts to be output changes, and this can be used as a signal mark reproduction signal. Further, (5Da + 5Db) − (5Dc + 5Dd) may be used as a reproduction signal by utilizing the fact that the distribution of light incident on the photodetector 5D changes depending on the position of the signal mark. Similarly, since the distribution of the incident light to the photodetector 5D changes even if the position 17a of the evanescent light is displaced in the direction of the arrow 21T, (5Da + 5Dd) − (5Db + 5Dc) may be used as a tracking error signal for the groove 20G. it can.
[0052]
If the polarization state of the incident light 4 is linearly polarized and its electric vector is in the direction of the arrow 4E in FIG. 2A, the TE mode is excited in the direction 15E orthogonal to the arrow 4E, and the parallel direction 15M TM mode is excited, and both are excited in the direction between them.
[0053]
The equivalent refractive index N of guided light varies depending on the waveguide mode. In general, the equivalent refractive index of the TE mode (guided mode in which the electrical vector of the guided light is parallel to the waveguide surface) is the TM mode (the electrical vector of the guided light is the waveguide surface). Larger than the equivalent refractive index of the non-parallel waveguide mode). Therefore, there is no guided light excitation in the 15M direction when the equivalent refractive index N of the guided light is equal to the equivalent refractive index of the TE mode, and there is no guided light excitation in the 15E direction when it is equal to the equivalent refractive index of the TM mode. If the guided light is excited in all directions in order to increase the light input efficiency, it is preferable to make the equivalent refractive indexes of the TE mode and the TM mode equal.
[0054]
[Second Embodiment]
FIG. 4A is a cross-sectional structure of the waveguide layer in the second embodiment of the present invention, and FIG. 4B is an explanatory view showing the equivalent refractive index of the waveguide layer. The wavelength of the light source is limited to this embodiment. Is set to 0.78 μm. The second embodiment is the same as the first embodiment except for the configuration of the waveguiding layer 7, and the description of the same parts is omitted.
[0055]
4A, the waveguide layer 7 has a three-layer structure in which a film having a high refractive index of 2.10 is sandwiched between films having a low refractive index of 1.75. A film having a refractive index of 2.10 is, for example, Ta ₂ O _Five The film can be formed by sputtering using as a target. A film having a refractive index of 1.75 is, for example, Ta. ₂ O _Five And SiO ₂ The film can be formed by sputtering the mixed target.
[0056]
4B, the vertical axis represents the equivalent refractive index, the horizontal axis represents the thickness d of the film having a refractive index of 2.10, the refractive index of the transparent layers 6 and 8 is 1.45, and the film has a refractive index of 1.75. The thickness of the upper and lower sides is 0.223 μm. When d = 0.16 μm, TE1 and TM1 have the same equivalent refractive index (see point A), and the curve of TE1 and the curve of TM1 come into contact with each other asymptotically, so there is a tolerance for d error. . Therefore, according to the second embodiment of the present invention, it is possible to make the equivalent refractive indexes of the TE mode and the TM mode equal.
The light use efficiency can be further increased than in the first embodiment.
[0057]
Note that a waveguide layer having a three-layer structure in which a low refractive index film is sandwiched between high refractive index films may be used.
[0058]
[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIGS. 5, 6A and 6B. FIG. 5 shows a cross-sectional structure of an information recording / reproducing apparatus in the third embodiment of the present invention. Compared to the first embodiment, the third embodiment is the same as the first embodiment except that the configuration of the grating and the photodetector is changed, and the description of the same parts is omitted.
[0059]
In FIG. 5, a transparent layer 6 having a low refractive index such as SiO 2 is formed on the surface of the transparent parallel substrate 5 on which the photodetector 5D is formed, and is concentric with an intersection O with the optical axis L as the center. The grating 6G is formed in the annular zone region surrounding the point O on the surface of the transparent layer 6. A waveguiding layer 7 is formed on the transparent layer 6 and other configurations such as the reflective layer 9 are the same as those in the first embodiment.
[0060]
The light 4 incident on and transmitted through the parallel substrate 5 is shielded on the side where the photodetector 5D is formed, but is incident on the waveguide layer 7 via the transparent layer 6 on the side where the photodetector 5D is not formed. The guided light 15 from the outer peripheral side toward the center O is excited by the grating 6G. Further, the component of the incident light that passes through the waveguiding layer 7 is reflected by the reflecting layer 9 and re-enters the waveguiding layer 7 so that a part thereof is coupled, so that the overall input efficiency is increased.
[0061]
Since the waveguide layer 7 is disconnected at the center position of the grating 6G and is in contact with the truncated cone portion 10 formed of a transparent medium having a higher refractive index than that of the waveguide layer at this position, the guided light 15 reaching the disconnection position. Is attracted from the waveguiding layer 7 to the inside of the truncated cone part 10 and becomes the light 16 gathered around the optical axis L, and a part thereof is an opening 9A (etched part of the reflective layer 9) on the bottom surface of the truncated cone part 10 After that, it leaks out as evanescent light 17 from the surface of the transparent layer 11.
[0062]
When the evanescent light 17 approaches the surface of the signal film 14, light energy flows out to the signal film 14 or light energy flows in the form of reflected light 18 from the signal film 14.
[0063]
When the signal film 14 is formed of a material whose reflectance changes due to light or heat, the signal mark 19 having a reflectance different from that of the surroundings can be recorded on the signal film 14 by the evanescent light 17. Further, the change in the state of the signal film 14 changes the amount of evanescent light 17 flowing out, and also changes the amount of reflected light 18 from the signal film 14. This change in the light inflow / outflow conditions changes the intensity of the guided light 15A (hereinafter referred to as feedback guided light) passing through the break position from the center to the outer peripheral side, and is emitted to the detector 5D side by the grating 6G. The intensity of 15B also changes. Therefore, the signal mark 19 can be detected by the photodetector 5D. Although the reflective layer 9 is used in the above embodiment, a film (mask layer) that changes from opaque to transparent by irradiation with strong light may be formed on the entire surface of the transparent layer 8 instead. Further, the mask layer may be formed on the transparent layer 11 of the above embodiment. In either case, the light quantity of the guided light 15 is small and the evanescent light is weak in a region away from the center, so that the mask layer is opaque and functions as a reflective layer. In the vicinity of the center, the light quantity of the guided light 15 is increased and the evanescent light is also strong, so that the mask layer becomes transparent and the evanescent light 17 can be led out.
[0064]
FIG. 6A shows a photodetector of an information recording / reproducing apparatus according to the third embodiment of the present invention, and FIG. 6B shows a configuration diagram of a signal surface as viewed from the light source side. In FIG. 6B, the signal surface on the disk substrate 13 is formed with a concavo-convex groove formed by a convex portion 20G and a concave portion 20L, and the convex portion 20G is close to the surface of the transparent layer 11. The position 17a of the evanescent light emitting portion from the surface of the transparent layer 11 is located at the center of the convex portion 20G, and this position 17a moves in the direction of the arrow 21S by the rotation of the disk substrate 13.
[0065]
As shown in FIG. 6A, the regions where the photodetectors are formed are on three sectors (5Da, 5Db, 5Dc) arranged every other one among six sectors that are equally divided by a straight line passing through the center O. Each detector is wired to the pads 22a, 22b, and 22c by a metal film such as Al, and detection signals are handed to the outside from these pads. Since the incident light 4 is blocked in the area of the photodetector, the guided light is excited by the grating 6G in the remaining three fan-shaped areas 15a, 15b and 15c.
[0066]
The guided light that passes through the waveguide layer 7 without leaking at the cut-off portion and the return guided light that is reflected in the signal surface and taken into the waveguide layer 7 passes through the central position O and then is transmitted by the grating 6G at that position. Radiated to detectors 5Da, 5Db, and 5Dc. The amount of radiated light, that is, the amount of light detected by the photodetector is determined by the positional relationship between the evanescent light 17 and the signal mark 19, and the position 17a passes over the signal marks 19a and 19b so that 5Da, 5Db, and 5Dc. The total amount of light detected at 1 changes, and this can be used as a signal mark reproduction signal. Further, assuming that one of the dividing lines of the detector is orthogonal to the arrow 21S, 5Da + 5Db-5Dc may be used as a reproduction signal by utilizing the distribution of the feedback guided light depending on the position of the signal mark. Similarly, since the distribution of the feedback guided light changes even if the position 17a of the evanescent light is displaced in the direction of the arrow 21T, 5Da-5Db can be used as the tracking error signal.
[0067]
For the third embodiment, As shown in FIG. Other forms of the shape of the photodetector are also conceivable. For example, the same effect can be obtained even if five sectors are arranged every other one out of 10 sectors that are equally divided by a straight line passing through the center O. .
[0068]
In the third embodiment, Since the fan area where the photodetector is formed and the fan area where the guided light is excited are separated, As in the first embodiment, scattered light from the guided light toward the center is Incident light detector Detected Without , Deviating from the propagation direction in the outbound path Since only the feedback guided light traveling toward the outer peripheral side can be detected, high-quality signal reproduction is possible as compared with the first embodiment.
[0069]
[Fourth embodiment]
FIG. 7A shows a photodetector of an information recording / reproducing apparatus in the fourth embodiment of the present invention, and FIG. 7B shows a configuration diagram of a signal surface as viewed from the light source side. The fourth embodiment is the same as the third embodiment except that the configuration of the photodetector is changed, and the other configurations are completely the same. The cross-sectional configuration diagram of FIG. 5 is the same as that of the third embodiment. The description of the same parts is omitted. In FIG. 7B, the signal surface on the disk substrate 13 is formed with concave and convex grooves by convex portions 20G and concave portions 20L, and the convex portions 20G are close to the surface of the transparent layer 11. The position 17a of the evanescent light emitting portion from the surface of the transparent layer 11 is located at the center of the convex portion 20G, and this position 17a moves in the direction of the arrow 21S by the rotation of the disk substrate 13.
[0070]
The region where the photodetector is formed is limited to four sectors (5Da, 5Db, 5Dc, 5Dd) arranged every other one among eight sectors that are equally divided by a straight line passing through the center O. The detector is wired to the pads 22a, 22b, 22c and 22d by a metal film such as Al, and a detection signal is handed to the outside from these pads. Since the incident light 4 is blocked in the region of the photodetector, the guided light is excited by the grating 6G in the remaining four fan-shaped regions 15a and 15b.
[0071]
After leaking from the waveguide layer 7 at the break, the guided light (feedback guided light) reflected by the signal surface and taken into the waveguide layer 7 passes through the center position O and then travels to the outer peripheral side. In particular, the feedback guided light propagating in the directions of the photodetectors 5Da, 5Db, 5Dc, and 5Dd is radiated to the photodetector by the grating 6G at that position. Since the propagation direction of the feedback guided light varies depending on the positional relationship between the evanescent light 17 and the signal mark 19, the position 17a passes over the signal marks 19a and 19b, and is detected at 5Da, 5Db, 5Dc, and 5Dd. The total amount of light changes, and this can be used as a signal mark reproduction signal. If the 5Dc and 5Dd symmetry lines are aligned in the direction of the arrow 21S, 5Da-5Db may be used as a reproduction signal by using the fact that the propagation direction of the feedback guided light changes depending on the position of the signal mark. . Similarly, since the propagation direction of the feedback guided light changes even if the position 17a of the evanescent light is displaced in the direction of the arrow 21T, 5Dc-5Dd can be used as the tracking error signal.
[0072]
For the fourth embodiment, As shown in FIG. Other forms of the shape of the photodetector are also conceivable. For example, the same effect can be obtained even with six sectors arranged at intervals of 12 sectors that are equally divided by a straight line passing through the center O. Since the fourth embodiment detects only the feedback waveguide light whose propagation azimuth is changed (that is, the component affected by the signal mark), high-quality signal reproduction can be achieved compared to the third embodiment. Is possible.
[0073]
[Fifth embodiment]
FIG. 8 shows a cross-sectional structure of an information recording / reproducing apparatus in the fifth embodiment of the present invention. The fifth embodiment is the same as the first embodiment except that the configuration of the optical coupling unit is changed, and the other configurations are the same, and the description of the same parts is omitted. In FIG. 8, a radiation light source 1 such as a semiconductor laser is fixed inside a holder 3 provided at the tip of a member 2 on a leaf spring. The radiation light source 1 emits light 4 having an axis L as an optical axis. A collimator lens 23 and a conical lens 24 are attached to the holder 3 coaxially with the optical axis L.
[0074]
The refractive index of the conical lens 24 is higher than the refractive index of the waveguide layer 7 to be described later, and a circular region having a diameter of about several tens of μm centered on the intersection O with the optical axis L of the photodetector 5D is formed on the bottom surface thereof. Is formed. On the lower surface of the conical lens, SiO ₂ A waveguide layer 7 is formed with a transparent layer 6 having a low refractive index interposed therebetween, and the other configuration is the same as that of the first embodiment, and thus the description thereof is omitted.
[0075]
Light converted to parallel light 4a by the collimating lens 23 Is The light 4b having a conical wavefront is refracted by the conical surface of the conical lens 24, enters the waveguide layer 7 through the transparent layer 6, and when the transparent layer 6 is sufficiently thin, the guided light 15 travels from the outer peripheral side toward the center. Excited. This excitation condition is that the refractive index of the conical lens 24 is n and the equivalent refractive index of the guided light is N, enter The angle of incidence is θ, and is given by the following formula (Formula 2).
[0076]
[Expression 2]
nsinθ = N (Formula 2)
The fifth embodiment differs from the first embodiment only in the optical coupling means for inputting light to the waveguide layer. The fifth embodiment is a grating 6G, but the fifth embodiment has a conical shape. It only changes to the lens 24. Accordingly, as in the first embodiment, signals can be recorded and reproduced on the signal surface, and light input by a prism (conical lens) is generally more efficient than light input by a grating. Light utilization efficiency higher than that of the form can be obtained.
[0077]
In addition, since the structure of the evanescent light emitting portion spreads over the surface as in the first embodiment, it also has a strong effect against thermal damage. Of course, a mask layer may be used instead of the reflective layer 9 as in the first embodiment, and the mask layer may be formed on the transparent layer 11. Furthermore, the three waveguide layers shown in the second embodiment and the detection methods shown in the third and fourth embodiments can be employed, and the same effect can be obtained. On the contrary, in the first to fourth embodiments, a system in which light is collimated by a collimator lens and incident on the grating may be used as in the fifth embodiment.
[0078]
In addition, there is also a method of using a change in the light emission characteristics accompanying increase / decrease in the amount of feedback light to the light source as a signal detection method. In this case, the detector 5D is unnecessary in the first to fifth embodiments, Instead, by monitoring the light emission characteristics of the light source (in the case of a semiconductor laser, fluctuations in the drive current value), the magnitude of the feedback light amount, that is, the presence or absence of a signal can be determined.
[0079]
In order to achieve isotropic light input coupling, it is conceivable to convert light from the light source into circularly polarized light by a quarter wavelength plate and input it to the waveguide layer. The formation may be omitted, and the grating 6G may be formed on the surface of the waveguide layer.
[0080]
In addition, the cut-off portion of the waveguide layer may have other forms than those described in the above embodiment as long as it has a function of leaking guided light propagating from the outer peripheral side to the center to the signal surface side. The shape 10 may be narrower toward the signal surface side, or a material having a lower refractive index than that of the waveguide layer may be used as a medium filling the truncated cone portion.
[0081]
The signal surface may be formed of a film used in a magneto-optical disk. Furthermore, the configuration in each embodiment of the present invention may be replaced.
In the first to fifth embodiments, the wave guide layer is formed on the plane. However, the wave guide layer may be formed on a curved surface. For example, the wave guide layer is formed on a conical surface. A disconnection portion may be provided at the apex position of the cone.
[0082]
【The invention's effect】
According to the above-described present invention, while the guided light is generated with high efficiency, the light can be concentrated while propagating in a low loss state in accordance with the guided mode, and the presence of the high refractive index truncated cone portion High energy light can be effectively derived on the signal surface as evanescent light, so that the light utilization efficiency can be greatly improved, and high density that exceeds the diffraction limit of light while maintaining a high information transfer rate. Can be recorded and reproduced.
[0083]
In addition, by relative movement with the signal surface in the state where the pressing force is applied, the surface of the waveguide layer can be stably levitation-scanned while maintaining a position close to the signal surface, and detection means provided in the vicinity of the waveguide layer Can efficiently detect the amount of reflected light from the signal surface and the amount of guided light propagating from the center to the outer periphery in the waveguide layer, so that the signal reproduction sensitivity can be greatly improved, Recognize tracks.
[0084]
In addition, since the structure of the evanescent light emitting part spreads across the surface, heat concentration does not easily occur and there is no deterioration due to thermal damage, and the evanescent light emitting part is stably placed close to the signal surface by a floating scanning method with an air layer in between. Scanning is possible, and the configuration as an apparatus is easy.
[0085]
Furthermore, changes in the evanescent light outflow conditions and changes in the amount of reflected light and feedback guided light can be detected by a detector close to the waveguide layer, greatly improving signal reproduction sensitivity and improving the evanescent light emitting section. Since the change in position affects the distribution and propagation direction of reflected light and feedback guided light, there is an effect that a signal mark or a track on the signal surface can be recognized by a difference in detection signal.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an information recording / reproducing apparatus according to a first embodiment of the present invention.
FIG. 2A is a plan view of a grating in the first embodiment of the present invention, and B is a light intensity distribution diagram for explaining light use efficiency of the grating.
FIG. 3A is a plan view of a main part of the photodetector in the first embodiment of the present invention, and B is a configuration plan view of a signal surface.
FIG. 4A is a cross-sectional configuration diagram of a waveguide layer in a second embodiment of the present invention, and B is an explanatory diagram showing an equivalent refractive index using the waveguide layer.
FIG. 5 is a cross-sectional configuration diagram of an information recording / reproducing apparatus in a third embodiment of the present invention.
FIG. 6A is a plan view of an essential part of a photodetector of an information recording / reproducing apparatus according to a third embodiment of the present invention, and B is a plan view of a signal plane.
FIG. 7A is a plan view of a principal part of a photodetector of an information recording / reproducing apparatus according to a fourth embodiment of the present invention, and B is a configuration plan view of a signal surface.
FIG. 8 is a cross-sectional configuration diagram of an information recording / reproducing apparatus in a fifth embodiment of the present invention.
FIG. 9 is a cross-sectional configuration diagram of a conventional information recording / reproducing apparatus.
FIG. 10A is a cross-sectional view of a main part of a conventional information recording / reproducing apparatus, and B is a light energy distribution diagram along a light propagation direction in the apparatus.
[Explanation of symbols]
1 Radiation light source
2 leaf spring
3 Holder
4 Synchrotron radiation
L Optical axis
5 Transparent parallel substrate
5D photodetector
5G grating
6 Transparent layer
6G grating
7 Waveguide layer
8 Transparent layer
9 Reflective layer
10 frustoconical part
11 Transparent layer
12 Air layer
13 Disc substrate
14 Signal membrane
15 Waveguide light
16 Concentrated light
17 Evanescent light
18 Reflected light
19 Signal mark

Claims

A radiation source, a transparent substrate, a waveguide layer configured on the surface of the transparent substrate opposite to the light source, and either the waveguide layer surface or the interface between the transparent substrate and the waveguide layer The optical coupling means having a concentric periodic structure centered on the optical axis of the light source, the waveguide layer is cut off at the center position of the periodic structure, and the light from the radiation light source is The optical coupling means excites guided light propagating from the outer peripheral side of the periodic structure to the center in the waveguide layer, and a part of the guided light is placed close to the waveguide layer at the disconnection position. An information recording / reproducing apparatus characterized by leaking to a signal surface on a flat substrate.

The transparent substrate is fixed on the same structure as the radiation light source, and the structure moves relative to the signal surface while being pressed against the signal surface by a pressing means. The information recording / reproducing apparatus according to claim 1 , wherein the information recording / reproducing apparatus floats across an air layer while facing each other.

The said waveguiding layer, the information recording and reproducing apparatus according to claim 1 in which the first transparent layer of lower refractive index than the waveguide layer are laminated.

4. The information recording / reproducing apparatus according to claim 3 , wherein a reflective layer is laminated on the first transparent layer at a position excluding the break position.

At the disconnection position, the disconnection part is covered with a second transparent layer having a higher refractive index than the waveguide layer, and the guided light in the waveguide layer passes through the second transparent layer to the signal surface side. The information recording / reproducing apparatus according to claim 1 , which leaks into the apparatus.

6. The information recording / reproducing apparatus according to claim 5, wherein a mask layer that changes from opaque to transparent upon irradiation with intense light is laminated on the second transparent layer.

6. The information recording / reproducing apparatus according to claim 5, wherein the cut-off portion has at least one shape selected from a conical shape and a truncated cone shape having the optical axis as a central axis.

Wherein at break position, the light leaked to the signal surface side of the waveguide layer, the information recording and reproducing apparatus according to claim 1 for recording a signal mark on said signal surface.

A photodetector is formed on or in the vicinity of the transparent substrate, and light leaking from the waveguide layer to the signal surface side at the disconnection position reflects the signal surface, and a part of the reflected light is detected by the light. detected by vessel, the information recording and reproducing apparatus according to claim 1 for reproducing a signal formed on the signal surface.

The information recording / reproducing apparatus according to claim 9 , wherein the photodetector is equally divided by a dividing line orthogonal to the moving direction of the signal plane, and a difference signal between the equal divisions is used as a reproduction signal.

A concavo-convex structure is formed on the signal surface along the moving direction of the signal surface, and the photodetector is equally divided by a dividing line along the moving direction. The information recording / reproducing apparatus according to claim 9, wherein the information recording / reproducing apparatus is a tracking control signal.

A light detector is formed on or near the transparent substrate, and light leaking from the waveguide layer to the signal surface side at the disconnection position is reflected on the signal surface and taken into the waveguide layer again. It becomes guided light propagating from the center of the periodic structure to the outer peripheral side in the waveguide layer, and at least one of the guided light or the light emitted from the waveguide layer is detected by the detector, on the signal surface The information recording / reproducing apparatus according to claim 1 , wherein the information recording / reproducing apparatus reproduces a signal formed on the signal.

13. The information recording / reproducing apparatus according to claim 12 , wherein the photodetector is composed of two parts sandwiching a straight line perpendicular to the moving direction of the signal surface, and a difference signal between the two detectors is used as a reproduction signal. .

A concavo-convex structure is formed on the signal surface along the moving direction of the signal surface, and the photodetector is composed of two parts symmetrical with respect to a straight line along the moving direction. 13. The information recording / reproducing apparatus according to claim 12 , wherein the difference signal is a tracking control signal.

Light leaking from the waveguiding layer to the signal surface side at the disconnection position reflects off the signal surface and is taken into the waveguiding layer again, and propagates in the waveguiding layer from the center of the periodic structure to the outer peripheral side. to be guided light, said waveguide light is fed back to the radiation source again, to claim 1 where the feedback by the detecting a change in the driving characteristics of the radiation source which generates and reproduces the signals formed on the signal surface The information recording / reproducing apparatus described.

2. The information recording / reproducing apparatus according to claim 1 , wherein the waveguide layer is formed of a multilayer film, and an equivalent refractive index of guided light propagating in the waveguide layer is substantially equal between the TE mode and the TM mode.

17. The information recording / reproducing apparatus according to claim 16 , wherein the multilayer film constituting the waveguide layer is formed in a three-layer structure in which a transparent layer having a high refractive index is sandwiched between transparent layers having a low refractive index.

The information recording / reproducing apparatus according to claim 16, wherein the multilayer film constituting the waveguide layer is formed in a three-layer structure in which a transparent layer having a low refractive index is sandwiched between transparent layers having a high refractive index.

Radiation light source, condensing means for converting light emitted from the radiation light source into parallel light, a transparent cone having the optical axis of the parallel light as a central axis, and a transparent buffer formed on a lower surface portion of the cone And a waveguide layer formed on the buffer layer, the waveguide layer being cut off at a position of a central axis of the cone, the refractive index of the cone, the refractive index of the waveguide layer, and the buffer The refractive index of the layer has a decreasing relationship in this order, and the parallel light is refracted on the conical surface of the cone and enters the waveguide layer through the buffer layer, and the outer peripheral side in the waveguide layer. The waveguide light propagating from the center axis side to the central axis side is excited, and a part of the waveguide light leaks to a signal surface on a flat substrate placed close to the waveguide layer at the disconnection position. Information recording / reproducing apparatus.

The cone is fixed on the same structure as the radiation source and the condensing means, and the structure moves relatively while being pressed against the signal surface by a pressing means, and this movement causes the waveguide layer to move. The information recording / reproducing apparatus according to claim 19 , wherein the surface floats across the air layer while facing the signal surface.

The information recording / reproducing apparatus according to claim 19 , wherein a first transparent layer having a lower refractive index than that of the waveguide layer is laminated on the waveguide layer.

The information recording / reproducing apparatus according to claim 21 , wherein a reflective layer is laminated on the first transparent layer at a position excluding the break position.

The disconnection portion is covered with a second transparent layer having a higher refractive index than the waveguide layer at the disconnection position, and the guided light in the waveguide layer leaks to the signal surface side through the second transparent layer. 20. The information recording / reproducing apparatus according to claim 19 .

24. The information recording / reproducing apparatus according to claim 23, wherein the cut-off portion has a conical shape or a truncated cone shape with the optical axis as a central axis.

The information recording / reproducing apparatus according to claim 19 , wherein a signal mark is recorded on the signal surface by light leaking from the waveguide layer to the signal surface side at the disconnection position.

A photodetector is formed on or near the lower surface portion of the cone, and light leaking from the waveguide layer to the signal surface side at the disconnection position reflects the signal surface, and a part of the reflected light is reflected. The information recording / reproducing apparatus according to claim 19 , wherein the information is detected by the photodetector and a signal formed on the signal surface is reproduced.

27. The information recording / reproducing apparatus according to claim 26 , wherein the photodetector is equally divided by a dividing line orthogonal to the moving direction of the signal surface, and a difference signal between the equal divisions is used as a reproduction signal.

An uneven structure along the moving direction of the signal surface is formed on the signal surface, the photodetector is equally divided by a dividing line along the moving direction, and the difference signal between the equal divisions is a tracking control signal. 27. The information recording / reproducing apparatus according to claim 26 .

A photodetector is formed on or near the lower surface portion of the cone, and light leaking from the waveguide layer to the signal surface side at the break position reflects off the signal surface and again enters the waveguide layer. The light is taken in and becomes guided light propagating from the center to the outer peripheral side in the waveguide layer, and at least one of the waveguide light or the light emitted from the waveguide layer is detected by the detector, The information recording / reproducing apparatus according to claim 19 , wherein the signal formed in the apparatus is reproduced.

30. The information recording / reproducing apparatus according to claim 29, wherein the photodetector is composed of two parts sandwiching a straight line orthogonal to the moving direction of the signal surface, and a difference signal of the two detectors is used as a reproduction signal.

An uneven structure is formed on the signal surface along the moving direction of the signal surface, and the photodetector is composed of two parts symmetrical with respect to a straight line along the moving direction, and the difference signal of the two detectors 30. The information recording / reproducing apparatus according to claim 29, wherein is a tracking control signal.

Light that leaks from the waveguide layer to the signal surface side at the disconnection position reflects off the signal surface and is taken into the waveguide layer again, and propagates in the waveguide layer from the center to the outer peripheral side. The information according to claim 19 , wherein the guided light is fed back to the radiation light source again, a change in driving characteristics of the radiation light source generated by the feedback is detected, and a signal formed on the signal surface is reproduced. Recording / playback device.

20. The information recording / reproducing apparatus according to claim 19 , wherein the waveguide layer is formed of a multilayer film, and an equivalent refractive index of guided light propagating in the waveguide layer is made substantially equal between the TE mode and the TM mode.

34. The information recording / reproducing apparatus according to claim 33, wherein the multilayer film constituting the waveguide layer is formed in a three-layer structure in which a high refractive index transparent layer is sandwiched between low refractive index transparent layers.

34. The information recording / reproducing apparatus according to claim 33, wherein the multilayer film constituting the waveguide layer is formed in a three-layer structure in which a transparent layer having a low refractive index is sandwiched between transparent layers having a high refractive index.